49.2. Archive Module Callbacks
The archive callbacks define the actual archiving behavior of the module. The server will call them as required to process each individual WAL file.
49.2.1. Startup Callback #
The
startup_cb
callback is called shortly after the
module is loaded. This callback can be used to perform any additional
initialization required. If the archive module has any state, it can use
state->private_data
to store it.
typedef void (*ArchiveStartupCB) (ArchiveModuleState *state);
49.2.2. Check Callback #
The
check_configured_cb
callback is called to determine
whether the module is fully configured and ready to accept WAL files (e.g.,
its configuration parameters are set to valid values). If no
check_configured_cb
is defined, the server always
assumes the module is configured.
typedef bool (*ArchiveCheckConfiguredCB) (ArchiveModuleState *state);
If
true
is returned, the server will proceed with
archiving the file by calling the
archive_file_cb
callback. If
false
is returned, archiving will not
proceed, and the archiver will emit the following message to the server log:
WARNING: archive_mode enabled, yet archiving is not configured
In the latter case, the server will periodically call this function, and
archiving will proceed only when it returns
true
.
Note
When returning
false
, it may be useful to append some
additional information to the generic warning message. To do that, provide
a message to the
arch_module_check_errdetail
macro
before returning
false
. Like
errdetail()
, this macro accepts a format string
followed by an optional list of arguments. The resulting string will be
emitted as the
DETAIL
line of the warning message.
49.2.3. Archive Callback #
The
archive_file_cb
callback is called to archive a
single WAL file.
typedef bool (*ArchiveFileCB) (ArchiveModuleState *state, const char *file, const char *path);
If
true
is returned, the server proceeds as if the file
was successfully archived, which may include recycling or removing the
original WAL file. If
false
is returned or an error is thrown, the server will
keep the original WAL file and retry archiving later.
file
will contain just the file name of the WAL
file to archive, while
path
contains the full
path of the WAL file (including the file name).
Note
The
archive_file_cb
callback is called in a
short-lived memory context that will be reset between invocations. If you
need longer-lived storage, create a memory context in the module's
startup_cb
callback.
49.2.4. Shutdown Callback #
The
shutdown_cb
callback is called when the archiver
process exits (e.g., after an error) or the value of
archive_library
changes. If no
shutdown_cb
is defined, no special action is taken in
these situations. If the archive module has any state, this callback should
free it to avoid leaks.
typedef void (*ArchiveShutdownCB) (ArchiveModuleState *state);